In general, a plasma etching apparatus is used for simultaneously etching an entire surface of a substrate to be processed by discharging an etching gas to the entire substrate from a plurality of gas discharge openings formed in parallel plate electrodes disposed above the substrate. However, recently, a demand for a local etching technique for locally etching a desired portion of a substrate is growing, and study and development thereof have been progressed.
Scaling up of a diameter of the substrate is also one of the reasons for causing the above demand. When the diameter of the substrate is scaled up, equipment costs increase. Further, it is difficult to uniformly supply a plasma on the entire substrate and maintain uniformity of the etching process. The fluidity of a reactant gas is one of the reasons that cause the non-uniformity. That is, a reactant gas is exhausted from a peripheral portion of the substrate, so that a flow speed of the reactant gas discharged from gas discharge openings increases as the reactant gas flows from the central portion of the substrate toward the peripheral portion of the substrate. Accordingly, it is difficult to uniformize the flow speed of the reactant gas on the entire substrate. The non-uniformity of the flow speed leads to non-uniformity in a density of the plasma generated on the substrate. Such non-uniformity increases as the diameter of the substrate increases.
In order to cope with the scaling up of the diameter of the substrate, there is suggested a method employing a local plasma to achieve a uniform etching process. For example, the following Patent Document 1 discloses a plasma processing apparatus and method in which a local plasma is generated and moved properly above an object to be processed, whereby the entire processing region of the object can be subjected to substantially constant plasma states.
[Patent Document 1] Japanese Patent Publication No. 3184682
However, the plasma processing apparatus of Patent Document 1 has following drawbacks. FIG. 5 shows a conventional plasma etching apparatus exemplified to explain the drawbacks thereof. As shown in FIG. 5, a pair of parallel plate electrodes 33a and 33b is provided inside a cover 28, and a first high frequency power is applied from an upper power supply 35 to the parallel plate electrodes 33a and 33b. The parallel plate electrodes 33a and 33b have therein gas channels, and a plurality of gas discharge openings 36 are formed in inner surfaces of the electrodes. A reactant gas is introduced from an inlet line 37, and discharged from the gas discharge openings 36 to a space between the facing parallel plate electrodes 33a and 33b. Next, the reactant gas is converted into a plasma by the high frequency power, and supplied toward a substrate to be processed such as a silicon wafer or the like. The substrate 15 is maintained by an electrostatic chuck 16 disposed above a susceptor 2, and a second high frequency power is applied from a lower power supply 38 to the susceptor 2.
When the local etching is carried out by the above plasma processing apparatus, it is preferable to etch only a lower portion (“A” portion in the drawing) of the cover 28. However, the reactant gas is exhausted from the periphery of the cover 28 and detours the substrate 15. Subsequently, a peripheral portion (“B” portion of the drawing) of the cover 28 is also slightly etched.
The etching of the “B” portion is unstable in an amount or a range of the reaction. Thus, when an entire substrate is etched by scanning the above plasma processing apparatus, non-uniformity occurs, which needs to be prevented. That is, there is required a local etching unit for etching only a desired portion (“A” portion) without etching other portions (while preventing other portions from being affected by the etching).